State song about most of region (7)
I believe the answer is:
arizona
'state' is the definition.
(Arizona is a US state)
'song about most of region' is the wordplay.
'song' becomes 'aria' (piece of music in an opera).
'about' means one lot of letters goes inside another.
'most of' means to remove the last letter.
'region' becomes 'zone' (zone is a kind of region).
'zone' with its last letter removed is 'zon'.
'aria' placed around 'zon' is 'ARIZONA'.
(Other definitions for arizona that I've seen before include "US state containing the Grand Canyon" , "American state, capital Phoneix" , "State of southern US" , "Site of Grand Canyon" , "State of SW US" .)